The term “biomass” includes many types of woody and herbaceous plant material, such as wood logs, slabs, chips, and bark; and agricultural residues such as corncobs, corn stover, sunflower shells and husks, nutshells, olive cake, and sugar cane bagasse. Biomass may also include the organic fraction of municipal solid wastes (including rubber tires), sewage sludge, manure, or other excrement, and the residues of animal husbandry, such as bones and carcasses. The term “inert” in the context of the present invention means that such compound, composition or material does not react with biomass, or its byproducts of pyrolysis, at temperatures and pressures attained within the reaction container in the practice of the present invention.
Charcoal is a carbonaceous solid with a fixed-carbon content of about 70 wt % or more. Charcoal is usually manufactured from hardwoods by pyrolysis in large kilns or retorts at temperatures below about 500° C. When charcoal is heated (“carbonized”) in an inert environment to temperatures typically above 800° C., it loses most of its remaining volatile matter and becomes a nearly pure carbon with a fixed-carbon content of 90 wt % or more. As used herein, the term “biocarbon” represents both charcoal and carbonized charcoal. Biocarbons possess many unique properties. Both charcoal and carbonized charcoal contain virtually no sulfur or mercury. Relative to their fossil fuel cousins, these biocarbons are very low in nitrogen and low in ash. Consequently, many carbonized charcoals are purer forms of carbon than most graphites. Unlike coking coals, pitches, crude resids, and other fossil carbon precursors, biomass does not pass through a liquid phase during pyrolysis at low heating rates. Consequently, biocarbons are inherently porous. They are also amorphous, as evidenced by very little of a turbostratic structure in their x-ray diffraction spectra. Nevertheless, a packed bed of carbonized charcoal conducts electricity nearly as well as a packed bed of graphite particles.
In U.S. Pat. No. 6,790,317, incorporated herein by reference in its entirety, a carbonization process to produce biocarbon is disclosed. The process of the present invention is an improvement over that process that significantly reduces the conversion times to biocarbon in similarly-sized reactors.
Accordingly, an object of the present invention is to provide an improved, rapid, efficient and economical process for converting biomass into charcoal.
This and other objects and advantages to the present invention will be readily apparent upon reference to the drawing and the following description.